In a machine tool including a tool rest which has a rotary shaft and is configured to allow a rotary tool such as an end mill to be coupled to the rotary shaft, a boring tool for boring operations may be coupled to the rotary shaft of the tool rest to machine internal surfaces of a workpiece. In this machining (boring) operation, the workpiece is typically placed with its one end supported at a headstock and its another end supported at a tailstock (or a second headstock with a sub-spindle) while the tool rest is disposed between the headstock and the tailstock (see, for example, JP 9-253902 A). The tool rest is retained in a position such that an axis of the rotary shaft of the tool rest is parallel to an axis of the main spindle of the headstock about which the workpiece supported on the main spindle is to be rotated.
When a boring operation is performed, as shown in FIG. 2, with a lathe 31 having a construction similar to that of the machine tool as described above, first, a tailstock 36 is moved away from the headstock 34, and a tool 32 for boring operations is installed in a headstock 33. It is to be noted that, when the tool 32 is installed, relevant parts of the lathe 31 are arranged such that the axis L1 of a rotating shank of the tool 32 is parallel to the axis L2 of the rotary shaft of the tool rest 33 and the axis L2 of the rotary shaft of the tool rest 33 (i.e., the axis L1 of the shank of the tool 32) is parallel to an axis C of rotation of a workpiece W (i.e., an axis of the main spindle of the headstock 34 around which the workpiece W supported on the main spindle is to be rotated). Thereafter, the tool rest 33 or the headstock 34 is moved in a direction of these axes of rotation for machining. A chuck 35 provided at the headstock 34 is configured to hold the workpiece W and rotate around the axis of the main spindle.
However, the conventional machine tool (lathe 31) as described above should be configured to allow the tailstock 36 to move a very long distance because the tailstock 36 should be moved away from the headstock 34 over the total distance of the length of the workpiece W plus the lengths of the tool 32 and the tool rest 33. This would require a large footprint of the machine tool, and entail its undesirable upsizing. Moreover, depending upon the shape of a workpiece W to be worked and the type of a tool 32 to be used, the tailstock 36 would necessarily be moved farther away from the headstock 34 so as to prevent the tool rest 33 from interfering with the tailstock 36, as the case may be. Thus, there is a need for improvement.
It would be desirable to provide a machine tool and a boring method in which interference of a tool rest with a supporting device provided in the machine tool to support a workpiece can be prevented and miniaturization of the machine tool can be achieved. The present invention has been made in an attempt to eliminate the above disadvantages, and illustrative, non-limiting embodiments of the present invention overcome the above disadvantages and other disadvantages not described above.